Strong Will is one of Fallout GURPS advantages. See: Fallout GURPS.
You have much more willpower than the average person. Your level of Will is added to your IQ when you make a Will roll (p. 24) for any reason, including any attempt to resist distraction, intimidation, seduction, torture, hypnosis or mystical attempts to take over your mind. However, this advantage does not help against combat shock and the like. In questionable cases, the GM's ruling is law. Cost: 4 points per +1 bonus.”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Strong Will was removed from the game.